The present invention relates generally to methods and apparatus for charging lubricant retaining and wicking material in consistent amounts, even when such material is readily compressible, into bearing lubricant reservoirs-including for example, bearing reservoirs of fractional horsepower motors.
In many material handling and moving applications, materials that are readily compressible or damaged are typically dispensed or metered by weight. On the other hand, materials that are pressurized and dispensed on a volume basis are either: (1) generally incompressible; (2) not adversely affected by pressurization or compression if they are in fact compressible; or (3) of a type such that non-consistent volumetric charges caused by compressive dispensing processes, are tolerable.
One specific area of technology in which the compressibility of a weight or volumetrically dispensed material is significant is that which involves dispensing compressible lubricant storage materials into bearing lubricant reservoirs for small electric motors or generators. In this type of application, small quantities of material are charged into the bearing lubricant reservoir, and excess material quickly causes problems--both during and after motor assembly. For example, excess material can cause problems ranging from those associated with cleaning up excess material at the dispensing station or subsequent motor assembly stations, to those associated with excess oil dripping from a finally assembled motor, or flowing into the motor interior. As will be understood, these conditions are unacceptable from handling and appearance standpoints and also because future leakage paths for oil from the reservoir may be established.
In the above-mentioned specific area of technology, the materials that may be satisfactorily used for the application are rather limited in number. This is explained in more detail hereinafter, but for the present it is noted that the material must be such that it satisfies motor lubricant lubricating characteristics, that a sufficient amount of oil is released at acceptable flow rates for an acceptable period of time, and so that the oil does not inadvertently drip out of the motor. Moreover, the materials known to applicant as acceptable for this type of application can easily be deleteriously affected as a result of mishandling during a compressive dispensing process.
Exemplary specific examples of extrudable or flowable lubricating materials particularly adapted for fractional horsepower motor use are those that are made according to the commonly assigned Whitt U.S. Pat. No. 3,894,956 dated July 15, 1975; and those made pursuant to Abel U.S. Pat. No. 2,966,459 of Dec. 27, 1960, the entire disclosures of which are incorporated herein by reference. These lubricating materials (also sometimes referred to as wicking materials) include a lubricant mixed with a lubricant retaining material-such material being referred to herein as a carrier or matrix material. Numerous problems arise in dispensing lubricating materials of this type because squeezing the material can cause the lubricant to flow out of the matrix. In fact, settling or separation of the oil from the carrier or matrix usually occurs with time simply due to bulk storage under static conditions.
The prior art recognizes and documents oil and matrix separation (as well as other metering problems) that occur when delivering this type of material to a metering or dispensing mechanism, and that also occur as the result of operation of the dispensing mechanism itself.
For example, Abel U.S. Pat. No. 3,053,421 (of Sept. 11, 1962) points out that variations in pressure exerted on extrudable wicking or lubricating materials can cause variations in "the ratio of the lubricating oil to the wicking material". Abel then goes on to describe by-pass or pressure relief valves and by-pass conduits, and a free piston metering device as important aspects of solving the separation problem. As another example, Tann U.S. Pat. No. 3,268,638 (of Aug. 23, 1966) stresses the separation problems associated with lubricant compositions of the type contemplated herein; and Tann suggests the use of vibratory techniques because of this problem.
The just-mentioned Tann patent illustrates what Tann describes as a metering and injection device wherein a pair of pistons are movable along a common bore. Material trapped between the two pistons is then dispensed into a lubricant reservoir or a bearing. The Tann arrangement, in addition to being one where the lubricant flow is not continuous (i.e., the flow is interrupted during each dispensing step); also provides for relative movement between the two pistons (which tends to separate the pistons) during a "retraction" stroke, with an injection or upper piston moving away from a lower or "metering head" piston. This relative movement in turn would appear to cause the creation of air pockets or voids between the co-acting end faces of the two pistons, or a suction which would tend to withdraw lubricant material in a reverse flow direction along a passage along the piston which forms the dispensing head or nozzle.
U.S. Pat. No. 3,221,948 to Kalist illustrates yet another structure wherein opposed movable pistons in a common bore are used to meter and dispense lubricating material. The structural elements used by Kalist are very similar to those of Tann, but the mode of operation of the Kalist structure is somewhat different from the Tann structure (discussed hereinabove). For example, with the Kalist approach, after a metered amount of lubricant has been dispensed, a lower piston associated with a dispensing head is moved in a "retracting" direction, and an upper piston is then moved in response to the movement of the lower piston. However, depending on which particular structure shown by Kalist is to be used (and in any event whenever the quantity of material actually dispensed is less than the maximum amount that could be dispensed) relative axial movement of the Kalist pistons will also occur. This relative movement with the Kalist structure is distinguished from the relative movement of Tann, in that the Kalist pistons tend to move toward one another and thus compress material trapped therebetween as the metering device retracts after material has been dispensed. This, in turn, can tend to cause oil per se or an oil-wicking mixture to exude from the metering head. This exuding material would be excess material that would cause the various problems mentioned hereinabove. In addition, any oil per se being exuded from the Kalist structure would alter the ratio of oil to matrix remaining in the Kalist structure.
At least the approach illustrated by Kalist has been utilized commercially long prior to the present invention and more than one year prior to this application. That commercially available equipment has included one or more cylinders having a pair of spaced apart movable pistons therein, and the separation between adjacent piston ends defines a volume intended to be substantially the same as the volume of a lubricant reservoir into which material is to be dispensed. The equipment under discussion also apparently follows the Kalist approach by using inlet and overflow ports in the cylinder side wall so that material may be supplied to a region between the two pistons through the inlet port and pass from such region through the outlet or overflow port. Thus, a substantially continuous circulation of material is maintained to assist in avoiding oil separation. In this equipment (as in the the Kalist patent), the material is transferred from the metering head to a workpiece by moving an upper piston so as to close off the overflow outlet, close the inlet port, and isolate a charge of material between the two pistons. Continued movement of the first piston compressively moves the oil/matrix material which in turn forces the lower piston to move until the lower piston exposes an outlet port. Thereupon the lower piston ceases movement, and continued movement of the first piston forces the charge of material through the outlet port to the workpiece.
Since the prior art mechanisms of which applicant is aware rely solely on axial motion for valving as well as injecting forces, and due to the inherent design of such mechanisms, the dispensing of material at inappropriate times in the form of material dribbling from the injection head can occur, resulting in a messy and wasteful operation, and potential departure from the desired proper oil to matrix ratio.
It should now be understood that it would be desirable to provide new and improved methods of metering extrudable lubricants, and apparatus useful in practicing such methods; so that precisely controlled amounts of such material may be metered, so that unwanted exudates may be minimized or eliminated, and so that unwanted separation of a lubricant and lubricant carrier is minimized, if not eliminated.